The present invention concerns a novel method and apparatus for surgically removing tissue from the cornea of an eye using an ablative laser, in which the accuracy and safety of the treatment is increased.
Ablative laser treatments occur in several areas in medicine including cosmetic laser skin resurfacing and excimer laser vision correction.
LASIK is a currently popular outpatient vision correcting excimer laser surgical procedure in which an excimer laser is used to remove tissue from the human cornea to change its shape. Each excimer laser pulse causes a photochemical reaction that sputters off a plume containing small amount of tissue. PRK and LASEK are variations of LASIK and all these procedures cause removal of microscopic amounts of tissue from the human cornea.
The laser treatment to correct myopia removes a disc shaped section of cornea. The disc has a prescribed diameter based on the settings of the laser. The thickness of the tissue removed is greater in the center of the disc and thinner toward the periphery. Another laser treatment known as phototherapeutic keratectomy or PTK is used to remove lesions and to change eye optics. In these laser treatments, an amount of the cornea tissue is removed to achieve the beneficial result.
To a large extent, inaccuracy in LASIK correction results from the variable response of corneal tissue to ablation by the laser. Because of the variable response, it is commonly necessary to reoperate to adjust for undercorrections or overcorrections. Many factors affect the actual amount of tissue removed including atmospheric humidity and pressure, patient age, variations in hormonal level, the variations in timing by different surgeons on different patients allowing a variable amount of tissue drying during the procedure, etc. Experienced surgeons can perform statistical studies on their data and can become more uniform in their procedures, but there is always some degree of patient-to-patient variation.
The material removed from the cornea during an excimer laser ablation is somewhat toxic to the surgical personnel in that the surgical personnel may breathe in aerosolized protein from another human. The protein may cause allergic reactions in the respiratory system. More seriously, the protein sputtered off the cornea of a patient could possibly carry viral particles and very tiny prions such as transmit hepatitis, Creutzfeld-Jakob disease (human xe2x80x9cmad cowxe2x80x9d disease), and possibly human immunodeficiency virus (which causes AIDS).
There are several methods to guard the surgeon against disease transmission including methods as simple as breathing through a snorkel tube to more involved methods which aspirate the material as it is sputtered off the cornea in the surgery. The problem with the devices that aspirate away particles is that moving air can introduce a drying action on the cornea and cause further inaccuracy to the laser treatment. However, aspiration of tissue removed from the cornea during surgery has been found effective to alleviate the potentially toxic reactions and also to alleviate the offensive odor that is common with laser surgery.
It is an object of the invention to provide a system for increasing the accuracy of ablative laser treatment of the cornea.
Another object of the present invention is to provide a system for analyzing removed living tissue during a laser ablation.
A further object of the invention is to provide a system for optimizing laser treatment of the human cornea using aspiration of the removed living tissue and quantitative analysis of the aspirated tissue.
A still further object of the present invention is to provide a system for surgically removing tissue from the cornea of an eye during an ablative laser treatment, which is simple to operate yet enables increased accuracy of ablative laser treatment.
Other objects and advantages of the present invention will become apparent as the description proceeds.
In accordance with one embodiment of the present invention, a method is provided for increasing the accuracy and safety of ablative laser treatments of the eye. An amount of tissue is removed from the cornea, using an ablative laser, thereby providing an effluent. The effluent is aspirated and quantitized. An estimated* actual optical change is computed, based upon input data relating to a dimension of the ablative cornea and the quantitized effluent. The estimated actual optical change is compared to a desired optical change, and the laser treatment is modified based upon the comparison of the estimated actual optical change to the desired optical change.
*The results of the computations are referred to herein as xe2x80x9cestimatedxe2x80x9d because of inherent imperfections in the effluent aspiration. 
In the illustrative embodiment, the input data relating to the dimension of the ablative cornea includes at least one of the radius, diameter, area and periphery of the ablated cornea. The estimated actual optical change is computed by a computer which may use various algorithms, including but not limited to the Munnerlyn formula.
In another embodiment of the present invention, an amount of tissue is removed from the cornea using an ablative laser, thereby providing an effluent. The effluent is aspirated and quantitized, and an estimated depth of tissue removed is computed based upon input data relating to a dimension of the ablated cornea and the quantitized effluent. The estimated depth of tissue removed is compared to a desired depth of tissue to be removed and the laser treatment is modified, based upon the comparison of the estimated actual depth of tissue removed to the desired depth of tissue to be removed.
In accordance with one embodiment of the present invention, an apparatus is provided for increasing the accuracy and safety of ablative laser treatments of the eye. The apparatus includes an ablative laser, an aspirator for aspirating the effluent from the cornea, a chemical analyzer for quantitating the amount of effluent that has been aspirated from the cornea, and a computer for receiving data relating to a dimension of the ablative cornea and for receiving the quantitized effluent collected.
In one embodiment of the invention, the computer is operative to estimate the actual optical change (number of diopters of treatment accomplished) based on the inputted dimension data and the quantitized effluent data. The estimated actual optical change is compared with a desired optical change to provide information to the operator (surgeon) to allow for further corrective action at the time of the original operation for the sake of greater accuracy of treatment.
In another embodiment, the computer is operative to estimate the depth of ablative tissue based on the inputted dimension data and the quantitized effluent data. The estimated depth of ablative tissue is compared with a desired depth of tissue to be ablated to provide information to the operator (surgeon) to allow for further corrective action for the sake of greater accuracy of treatment.
In the illustrative embodiment, the effluent is quantitated in a chemical analyzer and the input data relating to the size of the ablated cornea comprises input data relating to at least one of the radius, diameter, area, and periphery of the ablated cornea.
A more detailed explanation of the invention is provided in the following description and claims, and is illustrated in the accompanying drawings.